This invention relates in general to the deformation of metals which become superplastic at elevated temperatures and more particularly to an apparatus and process that employs infrared energy to heat such metals.
Titanium, while being quite difficult to work and likewise machine at ambient temperature, becomes superplastic near 1650.degree. F. Thus, it deforms quite easily, that is under relatively little force, once the superplastic characteristics have been acquired. Superplastic deformation has perhaps found its greatest usefulness in connection with making aircraft components from sheet titanium. However, titanium oxidizes quite readily at its superplastic temperature and special precautions must be undertaken to prevent this during the deformation.
Heretofore, sheet titanium has been rendered superplastic and deformed, by placing titanium sheet between steel platens, one of which has a contoured surface corresponding in configuration to that which is to be imparted to the titanium sheet. The platens are heated to about 1650.degree. F. by electrical resistance-type heating elements embedded within them, and at the same time the sheet is subjected to an inert environment, such as one composed of argon gas. The platens, being against the sheet titanium, conduct heat into the titanium and the temperature of the titanium rises until it corresponds to that of the platens. At this time, the pressure of the argon gas on the side of the sheet which is presented away from the contoured surface is elevated sufficiently to deform the titanium sheet against that surface, whereupon the sheet acquires the shape of the surface.
At 1650.degree. F., the platens glow a bright red and cannot be approached without wearing special protective clothing including a face shield. Moreover, special equipment is necessary to insert the flat titanium sheet between the platens and to thereafter remove the formed part. Indeed, the formed part is so hot that it cannot be handled manually, unless by one wearing heavily insulated gloves and then only for a few seconds. The necessity for the protective clothing and special handling equipment derives from the fact that the temperature of the platens remains at about 1650.degree. F., even while the apparatus is being loaded and unloaded, and indeed they must, for the platens have relatively large mass and do not change temperature readily. As a consequence, the heating elements within the platens consume an enormous amount of electrical energy.